1. Field of the Invention
The present invention relates to an image processor, an image processing method, a program that makes computer execute the method, and a recording medium.
2. Description of the Related Art
Most of the recent color copying machines have an auto color selection (ACS) function. The color copying machines include an automatic color mode for determining whether to perform color image output or monochrome image output automatically by the ACS function. The color copying machines are configured to enable an operator to specify a mode among a plurality of modes such as a color mode for performing color image output and a monochrome mode for performing monochrome image output on an operation panel.
According to the ACS, rough pre-scanning is performed before the actual scanning, to determine whether a document is a color document or a monochrome document. However, since image information can be recently stored in a memory of the copying machine, pre-scanning is not necessary as disclosed in Japanese Patent Application Laid-open (JP-A) No. 2001-119589. Accordingly, users do not feel stressed by the time required for copying.
JP-A No. H10-336466 discloses an image forming apparatus that performs analysis for presuming which mode a user is going to select, to determine an output mode, instead of simply classifying a document image into color and monochrome.
JP-A No. 2001-352453 discloses a technique for performing image processing, taking into consideration an instance that a color document is reproduced in a monochrome image. The technique attempts to dissolve a problem in that characters on halftone dots cannot be read due to a weak contrast depending on colors, because of reproduction of the color document in a monochrome image by controlling the contrast in accordance with color edges.
In the case of the automatic color mode, the color image output is selected only when a document is a color document, and the monochrome image output is selected only when the document is a monochrome document. However, in the case of color mode, the document to be copied may not be limited to the color document, and in the case of monochrome mode, the document to be copied may not be limited to the monochrome document. With a color copying machine installed in stores such as convenience stores, the cost of color copy per one sheet is more expensive than the monochrome copy. Even in a case of a color document, if a monochrome copy is enough, the monochrome mode can be selected, in view of the cost. However, the technique disclosed in JP-A No. 2001-119589 does not correspond to such cases.
The technique disclosed in JP-A No. H10-336466 is based on the recognition that the selection of the color/monochrome output mode performed by a user is not simply based on the document type of color/monochrome. However, according to the presumption based on the analysis, it is difficult to set image formation appropriately.
According to the technique in JP-A No. 2001-352453, clear reproduction of characters has generally the highest priority in the monochrome mode. However, in the case of a color document, a pattern document formed of halftone dots with lines as large as about 175 must be presumed. Therefore, processing that does not harm the tone and processing that can obtain reproduced images with fidelity to original documents are desired. On the other hand, in the case of the monochrome document, the tone is not important as in the color document, and it is necessary to presume documents in which the highlighted side of the document is rough or isolated dots are present, such as dot document with about 100 lines represented by newspaper or binary printer output images, and hence, processing that can reproduce characters clearly while skipping highlighted dots is desired. However, the technique in JP-A No. 2001-352453 has a problem in that these demands cannot be satisfied.